先进制造技术双语2课件.ppt

1、AUTOMATED MANUFACTURINGCHAPTER 22.1 CAD/CAM 2.1.1 CAD/CAM Defined CAD: The use of computer systems to assist in the creation, modification, analysis, or optimization of a design. A CAD model of a mouse. CAM: The use of computer systems to plan, manage, and control the operations of a manufacturing p

2、lant. Two kinds of CAM: (1) Computer monitoring and control direct application of computer in the process. (2) Computer manufacturing support applicationsindirect application.Computer ProcessProcessDataMonitoringComputer ProcessDataControl Control SignalsProcessFormability Analysis ExampleMold and T

3、ooling Example. CAD/CAM means using computers in the design and manufacturing processes. Since the advent of CAD/CAM, other terms have developed.Computer graphics (CG)Computer-aided engineering (CAE)Computer-aided design and drafting (CADD)Computer-aided process planning (CAPP) A key goal of CAD/CAM

4、 is to produce data that can be used in manufacturing a product while developing the database for the design of that product. When successfully implemented, CAD/CAM involves the sharing of a common database between the design and manufacturing components of a company. CAD/CAM grows out of a need to

5、continually improve productivity, quality, and, in turn, competitiveness. There are also other reasons why a company might make a conversion from manual processes to CAD/CAM: (1) Increased Productivity (2) better quality (3) better communication2.1.1 Rationale for CAD/CAM(4) common database with man

6、ufacturing(5) reduced prototype construction costs(6) faster response to customers A prototype is an original type, form, or instance of something serving as a typical example, basis, or standard for other things of the same category. (1) Increased Productivity Productivity in the design process is

7、increased by CAD/CAM. The amount of time required to document a design can be reduced significantly with CAD/CAM. These means a shorter design cycle, shorter overall project completion time, and a higher level of productivity. (2) Better Quality Because CAD/CAM allows designers to focus more on actu

8、al design problems and less on time-consuming, nonproductive tasks, product quality improves with CAD/CAM. labor-intensive tasks are performed by the computer, fewer design errors occur. These all lead to better product quality. (3)Better Communication Design documents such as drawings, parts lists,

9、 bills of material, and specifications are tools used to communicate the design to those who will manufacture it. Because CAD/CAM leads to more uniform, standardized, and accurate documentation, it improves communication. (4)Common Database With CAD/CAM, the data generated during the design of a pro

10、duct can be used in producing the product. This sharing of a common database helps to eliminate the age-old wall separating the design and manufacturing functions (5) Reduced Prototype Costs With CAD/CAM, 3-D computer models can reduce and, in some cases, eliminate the need for building expensive pr

11、ototypes. Such CAD/CAM capabilities as solids modeling allow designers to substitute computer models for prototypes in many cases. (6)Faster Response to Customers Response time is critical in manufacturing. By shortening the overall design cycle and improving communication between the design and man

12、ufacturing components, CAD/CAM can improve a companys response time. All design tasks accomplished using a computer fall into one of four broad categories: (1)Design Modeling In CAD/CAM design modeling, a geometric model of a product is developed that describes the part mathematically. The geometric

13、 model also allows the graphic image to be easily edited and manipulated once displayed.2.1.2 Computers and Design (2) Design Analysis Once a proposed design has been developed, it is necessary to analyze how it will stand up to the conditions to which it will be subjected. Such analysis methods as

14、heat transfer and stress-strain calculations are time-consuming and complex. With CAD/CAM, special computer programs written specifically for analysis purposes are available. One such program is finite-element analysis. FEA involves breaking an object up into many small rectangular or triangular ele

15、ments, then analyzing each individual element by computer. By analyzing the response of each finite element of the object to the stress, strain, heat, or other force acting on it, the computer can predict the reaction of the whole object. Modern CAD/CAM systems with FEA capability make the process s

16、imple to achieve.FEA RepresentationMises stressTemperature fieldTemperature stress (3) Design Review The first is the semiautomatic dimensioning capability of many CAD/CAM software packages. The layering capability of CAD/CAM software also simplifies design review. Another CAD/CAM software capabilit

17、y that has simplified design review is called interference checking. With Kinematic capability, CAD/CAM software can simulate motion on CRT/LED display. (4) Design Documentation With CAD/CAM, the drawings needed to document the design can be produced using the database created during the design proc

18、ess. Because the computer can store the mathematical models of all drawings done on a CAD/CAM system, once a drawing has been produced, it never has to be redrawn. It can simply be called up from storage, entered into the appropriate location in the drawing package, and used again and again.The real

19、 interface is the common database they share. What is DFA?DFA methodologies were developed to support the designer by generating feedback on the consequences of design decisions on product assembly. The aim is to help the designer to produce an efficient and economic design.2.1.4 Design for Assembly

20、, Manufacturing, and the Environment (DFA/M/E) The application of DFA guides the designer towards a product with an optimum number of parts, that requires simple, cost-effective assembly operations and the most appropriate manufacturing processes and materials for its components. In general, the des

21、igner is guided through the analyses, which are presented in a series of assessment charts. The charts are based on empirical data gathered by knowledge engineering exercises with industrial experts and organised in an easy-to-use worksheet format. During the evaluation, the designer is required to

22、assess component functionality, form manufacturing processes and assembly characteristics using values extracted from the charts according to component properties. These numbers are then compiled in tabular format, and calculations performed. In this way, the designer is able to quantify the suitabi

23、lity of the design. The Lucas DFA Methodology has been chosen for use within the Designers Sandpit project because of existing expertise within the group.The Designers Sandpit is an assembly-oriented design environment containing tools and techniques to generate economic designs. As part of this env

24、ironment, designers need methods for assessing the assembliability of their designs.The Lucas DFA method was developed in the early 1980s by the Lucas Corp. in the U.K. The method is based on three separate and sequential analyses: Specification, Design ,Functional analysis. What is DFM? Followed du

25、ring the design process, DFM is an approach which has the aim of improving manufacturing productivity. It brings major benefits when used during the design of new generations of products. It is a method of working which: Helps the team focus on clear and common objectives Encourages problem-ownershi

26、p and prevents manufacturing problems being shifted from area to area (e.g. from direct to overhead costs) Uses a top-down approach (preventing early and wasteful focus on detail) to product design During DFM, the considerable background work required for the conceptual phases is compensated for by

27、a shortening of later development phases.Problem ownership: Willingness to accept ownership and responsibility What is Design for the Environment? Design for the Environment (DFE) is the consideration of pollution prevention and resource conservation within the design process. DFE starts with the de

28、velopment of environmental goals within an example set of environmental policy, needs, and concern categories. Goals should be large in scope: considering the full life cycle of performance, cost, and environmental implications. There are three major elements of design for the environment: design fo

29、r environmental manufacturing, design for environmental packaging, and design for disposal and recycleability. Design for environmental manufacturing involves the following considerations:Non-toxic processes & production materials Minimum energy utilization Minimize emissions Minimize waste, scrap &

30、 by-products Design for environmental packaging involves the following considerations:Minimum of packaging materials Reusable pallets, totes and packaging Recyclable packaging materials Bio-degradable packaging materials Design for disposal & recycleability involves the following considerations:Mate

31、rial selection to enable re-use and minimize toxicity Minimum number of materials / colors to facilitate separating materials and re-use Material identification to facilitate re-use Design to enable materials to be easily separated Design for disassembly New techniques to analyze a particular design

32、 for its manufacturability include the design for manufacturing and assembly (DFMA) software tools by Boothroyd and Dewhurst (1999). A suite of tools is available that contain, for example, DFM software for machining, DFM software for sheet metalworking, DFE software to assess environmental impacts,

33、 and their best-known DFA module for evaluating assembly. The DFA for assembly module involves two key ideas: The quality of individual subcomponents must be high. Also, their number must be reduced as much as feasible. Assembly operations must be as simple as possible. For example, factory layouts

34、should be orderly, the shape of individual components should be simple, design features should simplify the assembly of one component with another, and assembly operations should not fight gravity. DFM for machining module Machining for Windows assists a designer with the following issues: developin

35、g operation and process plans, obtaining cost estimates at the earliest stages of conceptual design, developing quotations, and planning for production. One of the most fundamental concepts in the area of advanced manufacturing technologies is numerical control (NC). The variety demanded in view of

36、the varying tastes of the consumer calls for very small batch sizes. Small batch sizes are not able to take advantage of mass production techniques such as special purpose machines or transfer lines.2.2 Numerical Control There is a need for flexible automation where you can get the benefits of rigid

37、 automation and also be able to manufacture a variety of products, thus bringing in flexibility. The method of numerical control is appropriate for this purpose, and in future manufacturing is expected to be increasingly dependent on numerical control. NC has been defined by the Electronic Industrie

38、s Association (EIA) as “a system in which actions are controlled by the direct insertion of numerical data at some point. The system must automatically interpret at least some portion of this data. ” The numerical data required to produce a part is known as a part program. A numerical control machin

39、e tool system contains a machine control unit (MCU) and the machine tool itself. The MCU is further divided into two elements: the data processing unit (DPU) and the control loops unit (CLU). The DPU processes the coded data from the tape or other media and passes information on the position of each

40、 axis, required direction of motion, feed rate, and auxiliary function control signals to the CLU. The CLU operates the drive mechanisms of the machine, receives feed back signals concerning the actual position and velocity of each of the axes, and signals the completion of operation. The DPU sequen

41、tially reads the data. When each line has completed execution as noted by the CLU, another line of data is read. A data processing unit consists of some or all of the following parts: (1) Data input device such as a paper tape reader, magnetic tape reader, RS232-C port, etc(2) Data-reading circuits

42、and parity-checking logic(3) Decoding circuits for distributing data among the controlled axes(4) An interpolator, which supplies machine-motion commands between data points for tool motion A control loops unit, on the other hand consists of the following:(1) Position control loops for all the axes

43、of motion, where each axis has a separate control loop(2) Velocity control loops, where feed control is required(3) Deceleration and backlash take up circuits(4) Auxiliary functions control, such as coolant on/off, gear changes, spindle on/off control Numerical control machines are more accurate tha

44、n manually operated machines, they can produce parts more uniformly, they are faster, and the long-run tooling costs are lower. The development of NC led to the development of several other innovations in manufacturing technology:Electric discharge machiningLaser-cuttingElectron beam welding Numeric

45、al control has allowed manufacturers to undertake the production of products that would not have been feasible from an economic perspective using manually controlled machine tools and processes.A factory worker in 1940s Fort Worth, Texas. Numerical control or control by numbers, is a concept which h

46、as revolutionized the manufacturing scene. This is partially due to the rapid advancement in microelectronics that has taken place since late 1960s. The key factor responsible for the popularity of Numerical Control is the flexibility it offers in manufacturing.2. 2.1 Historical Development of NC Li

47、ke so many advanced technologies, NC was born in the laboratories of the Massachusetts Institute of Technology. The concept of NC was developed in the early 1950s with funding provided by the U.S. Air Force. In its earliest stages, NC machines were able to make straight cuts efficiently and effectiv

48、ely. Towards end of the second world war, there was increased activity in aerospace manufacturing in USA. John Parsons of Parsons Corporation which was one of the sub contractors to USAF (United States Air Force), was toying with the idea of utilizing digital computers which were then becoming popul

49、ar. Machining (milling) of complex curvature was a highly skilled job. Parsons proposed that the co-ordinate points of a complex three dimensional profile may be utilized for controlling the milling machine table so that accurate jobs could be produced. The USAF accepted his proposal and a contract

50、was awarded to him to develop such a machine. The project was then awarded to the Servomechanism Laboratory of Massachusetts Institute of Technology in 1951, who finally demonstrated a working milling machine in 1952, This was a Cincinnati Hydrotel Vertical Spindle milling machine with a controller